1. Field of the Invention
The present invention relates to multi-layer molded polymer compositions and their methods of manufacture. More specifically, the invention relates to multi-layer polymer compositions having a first polyolefin layer and a second polymer layer made of dissimilar and immiscible materials joined together using a compatibilizer.
2. Description of the Related Art
It is useful to manufacture containers, films, tubing and packaging from multi-layer materials. The different materials provide different properties. By combining these different materials, the final product will have the benefits of materials in the individual layers. Unfortunately, materials that provide unique physical properties often do not adhere well to other materials having other different physical properties. In these cases, an intermediate adhesive layer is used to join the dissimilar materials. The need for an adhesive increases the cost and complexity of fabricating the multi-layer compositions.
One example of this can be seen in the manufacture of packaging and containers having permeation resistant qualities. U.S. Pat. No. 4,973,625 teaches a method of manufacturing composite structures having an oxygen barrier intermediate various high density polyethylene layers (HDPE). The oxygen barrier is made from ethylene vinyl alcohol (EVOH). EVOH is generally immiscible in HDPE and visa versa. EVOH does not adhere well to the HDPE and therefore may not be co-extruded directly against the HDPE layer. The U.S. Pat. No. 4,973,625 patent teaches the use of intermediate bonding resin to unite the multi-layer structure. In this example, a melt-extrudable bonding resin of amorphous polycarboxylamide serves as a tie layer between the HDPE and EVOH. A similar construction has been used in the manufacture of blow molded fuel tanks to provide permeation resistance to low molecular hydrocarbons. Unfortunately, this construction requires the extrusion of intermediate tie layers between the polyolefin layer and the barrier layer. When used in blow molded fuel tanks, five or more separate extruders are needed to make the multi-layer fuel tank wall. Two or more extruders may be eliminated if the intermediate adhesive layer between the polyolefin and barrier layer is eliminated. Therefore, it is an object of the present invention to provide a composition for manufacturing multi-layer molded polymer articles using dissimilar materials without the need for an intermediate adhesive tie layer.